Refractory Metal Nitride Encapsulation for Copper Wiring

Abstract

Recent interest in copper-based metallization for ultra fast logic devices has stimulated extensive studies on thermal stability issues, as well as the search for novel deposition and etching processes. In copper wiring technology, thermal stability problems include: (1) rapid diffusion of copper into dielectric substrates, (2) low-temperature reaction with most near-noble metals and their silicides, (3) the susceptibility of copper to oxidation, (4) poor adhesion characteristics of copper on most dielectric materials, and (5) thermal-stress-induced void formation and cracking. The basic issues have been summarized in a recent review.When copper is in contact with a silicon substrate, copper can diffuse into active regions of devices where it becomes a recombination-generation center. In addition, copper forms the silicide Cu₃Si by reacting with the substrate at temperatures less than 200°C. After the formation of the Cu₃Si phase, the underlying silicon in the Cu₃Si/Si structure is readily oxidized even at room temperature. In the case of copper in contact with silicon dioxide under bias thermal stress (BTS), copper is found at the SiO₂/Si interface under a positive electric field. Copper diffusion in doped glass, e.g., phosphosilicate glass and silicon nitride films, is a factor at temperatures below 400°C.